(Chicago Sun-Times) — Mandatory minimum sentences, touted by some as a cure for gun crimes, are little more than a power grab by prosecutors.

The intent of a mandatory minimum sentence is to make sure that people convicted of certain serious crimes get prison time and not a slap on the wrist, such as probation. But in the real world, that’s not what happens.

In the real world, this is what happens: Mandatory minimums, dictated by law, make it impossible for judges to use common-sense discretion when imposing sentences, so judges must nail some poor sap who simply made a foolish mistake with the same harsh sentence they would impose on a hardened criminal. But those mandatory minimums do nothing to reduce the ability of prosecutors to use discretion when deciding what charges — light or heavy — to file against a defendant. The indirect result is that prosecutors, not judges, set the sentence.

Mandatory sentencing is a fiction. It simply takes the decision-making for sentencing away from judges sitting in open court, where their actions can be questioned by higher courts, and hands that huge power and responsibility to prosecutors, who make their decisions behind closed doors, never to be challenged.

Legislation that might be called to a vote this week in Springfield would triple Illinois’ mandatory minimum sentence from one to three years for people convicted of the illegal use of a weapon, and it would broaden the kinds of crimes covered. An earlier version advanced out of committee in the spring legislative session, but ultimately died. The bill is backed by Mayor Rahm Emanuel, Police Supt. Garry McCarthy and the families of some gun crime victims. McCarthy says 108 shootings or murders so far in 2013 would have been prevented had the bill already been a law this year. He cited the case of Bryon Champ, convicted in 2012 of the unlawful use of a weapon, who is accused of taking part in a September drive-by shooting that injured 13 in Chicago’s Cornell Square Park.

Clearly, we all wish Champ — if in fact he was one of the drive-by shooters — had still been behind bars.

But what about other sorts of gun-possession offenders who would qualify for same mandatory minimum sentence?

Would we really send an 87-year-old woman who lives in a dangerous neighborhood to prison for three years for illegally keeping a gun as protection? Should state Sen. Donne Trotter really have gone to prison for three years when a gun was found in his luggage at O’Hare Airport?

It’s a question that will come up more often in Illinois when the concealed carrying of weapons becomes legal next year, and people ­ — forgetting they are armed — try to carry guns into prohibited places. Should those people go to prison for three years as well?

The thinking behind mandatory minimum sentences is that prosecutors can be better trusted than judges to mete out tough punishment. Cook County State’s Attorney Anita Alvarez criticizes judges for being “quite lenient.” But most judges in the criminal court system are former prosecutors. And from 2010 through 2012, about 14,000 people were charged in three categories of unlawful use of a weapon, but the number of convictions was less than half of that. Changing sentences in cases where there is no conviction wouldn’t make any difference.

In analyzing the bill, the University of Chicago Crime Lab estimated that putting more people in prison would lead to 3,800 fewer crimes per year, including 400 fewer serious violent crimes.

But the Sentencing Policy Advisory Council calculates that had the stricter mandatory minimum law been in effect from 2010 through 2012, it would have boosted prison costs by about $393 million. A Department of Corrections note attached to the legislation last spring estimated the bill would result in an increase of 3,860 inmates, with additional operating costs of $701,712,300 and construction costs of $263,130,300 over 10 years. That money would have to come from somewhere. If that leads to smaller police forces or cutting out effective programs to prevent recidivism, we might wind up with more gun crime than before.

Julie Stewart, president of Washington-based Families Against Mandatory Minimums, noted in a Feb. 17 Chicago Sun-Times op-ed that Chicago’s murder rate actually jumped 16 percent after Illinois imposed its current one-year mandatory minimum in 2011. And a report released Thursday by the Northwestern School of Law Bluhm Legal Clinic concludes mandatory sentences would not deter crime.

Cook County Board President Toni Preckwinkle says tougher sentences are not the answer to crime.

“Jail is at the intersection of racism and poverty in this country,” Preckwinkle told the Chicago Sun-Times Editorial Board earlier this month.“This also involves race and class, and it’s hard to talk about it.”

Preckwinkle criticizes Alvarez’s office for always rejecting requests for bond reductions and not declining to prosecute cases with insufficient evidence brought in by Chicago police.

On the national level, the Obama administration is trying to curb mandatory minimum sentencing, which is an idea that goes back to the 1980s. Illinois should be doing so as well.